090 STATE BOARD OF AGRICULTURE. 



BRIEF REVIEW OF PREVIOUS REPORT. 



The investigation on the specific heat of soils showed that the magni- 

 tude of this property was about the same for all types of soil, namely 

 gravel, sand, humus loam, clay and peat; this being true both by equal 

 weight as well as by equal volume. By equal weight the magnitude of 

 the value was about 0.200°O and by equal volume about 0.500°C. The 

 specific heat of peat was only about one-half as great as that given to it 

 by previous investigators. 



It was concluded that in view of this remarkable equality of the specific 

 heat of the diverse types of soil, this factor exercised practically no in- 

 fluence in causing and maintaining a difference in temperature in these 

 various soils. 



Since, however, these diverse types of soil contain different amounts 

 of water, on account of the marked variation in their water-holding ca- 

 pacity, and water possesses five times as great specific heat as the dry 

 soils by equal weight or two times as great by equal volume and its latent 

 heat of evaporation and heat of fusion are tremendously high, it was con- 

 cluded that the water content of the soil is one of the chief intrinsic fac- 

 tors which might cause a variation in the temperature of these various 

 classes of soil. 



The phenomen of heat conductivity was measured in different types 

 of soil, (1) in their dry condition, (2) in their natural state under 

 laboratory conditions and (3) in their natural state under field condi- 

 tions. It was found that in all these three states the magnitude of 

 heat transference was markedly different in the various types of soil 

 but the order was always the same, namely, gravel manifested the highest 

 heat-transmitting power followed in order by sand, clay, loam and peat, 

 respectively. 



It was concluded, however, that even though these diverse classes 

 of soil possess markedly different abilities to propogate heat, yet this 

 factor of heat conductivity is only of secondary and not of primary im- 

 portance in the control and variation of their temperature. In other 

 words heat conductivity is not a dominant factor and the small varia- 

 tion in average temperature that it would cause in the different types of 

 soil under normal conditions is neutralized or offset by other contrary 

 factors and consequently as an agent itself it cannot cause a permanent 

 variation in average temperature in those soils which possess it in 

 different degrees. O'r if it is a dominant factor it opposes some other 

 contrary factor and causes those soils which possess it to the highest 

 degree to have the same average temperature as those that contain it in 

 the least extent. 



Under special circumstances, however, such as when a mulch is formed 

 on a cultivated soil heat conductivity might exert a slight predominating 

 and controlling infiuence on the soil temperature. In such a case, how- 



